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Implement PR1786 by iterating between dead cycle elimination 

and simplifycfg in the rare cases when it is needed.

llvm-svn: 44044
This commit is contained in:
Chris Lattner 2007-11-13 07:32:38 +00:00
parent 36d5575660
commit 61ce4dff7a
2 changed files with 163 additions and 33 deletions
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96
llvm/lib/Transforms/Scalar/SimplifyCFG.cpp
View File

@ -27,6 +27,7 @@
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Pass.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
@ -50,9 +51,9 @@ FunctionPass *llvm::createCFGSimplificationPass() {
}
static bool MarkAliveBlocks(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 16> &Reachable) {
SmallPtrSet<BasicBlock*, 128> &Reachable) {
std::vector<BasicBlock*> Worklist;
SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
bool Changed = false;
while (!Worklist.empty()) {
@ -93,42 +94,46 @@ static bool MarkAliveBlocks(BasicBlock *BB,
return Changed;
}
// It is possible that we may require multiple passes over the code to fully
// simplify the CFG.
//
bool CFGSimplifyPass::runOnFunction(Function &F) {
SmallPtrSet<BasicBlock*, 16> Reachable;
/// RemoveUnreachableBlocks - Remove blocks that are not reachable, even if they
/// are in a dead cycle. Return true if a change was made, false otherwise.
static bool RemoveUnreachableBlocks(Function &F) {
SmallPtrSet<BasicBlock*, 128> Reachable;
bool Changed = MarkAliveBlocks(F.begin(), Reachable);
// If there are unreachable blocks in the CFG...
if (Reachable.size() != F.size()) {
assert(Reachable.size() < F.size());
NumSimpl += F.size()-Reachable.size();
// Loop over all of the basic blocks that are not reachable, dropping all of
// their internal references...
for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB)
if (!Reachable.count(BB)) {
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI!=SE; ++SI)
if (Reachable.count(*SI))
(*SI)->removePredecessor(BB);
BB->dropAllReferences();
}
for (Function::iterator I = ++F.begin(); I != F.end();)
if (!Reachable.count(I))
I = F.getBasicBlockList().erase(I);
else
++I;
Changed = true;
}
if (Reachable.size() == F.size())
return Changed;
assert(Reachable.size() < F.size());
NumSimpl += F.size()-Reachable.size();
// Loop over all of the basic blocks that are not reachable, dropping all of
// their internal references...
for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB)
if (!Reachable.count(BB)) {
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI!=SE; ++SI)
if (Reachable.count(*SI))
(*SI)->removePredecessor(BB);
BB->dropAllReferences();
}
for (Function::iterator I = ++F.begin(); I != F.end();)
if (!Reachable.count(I))
I = F.getBasicBlockList().erase(I);
else
++I;
return true;
}
/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
/// iterating until no more changes are made.
static bool IterativeSimplifyCFG(Function &F) {
bool Changed = false;
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
// Loop over all of the basic blocks (except the first one) and remove them
// if they are unneeded...
//
@ -140,6 +145,31 @@ bool CFGSimplifyPass::runOnFunction(Function &F) {
}
Changed |= LocalChange;
}
return Changed;
}
// It is possible that we may require multiple passes over the code to fully
// simplify the CFG.
//
bool CFGSimplifyPass::runOnFunction(Function &F) {
bool EverChanged = RemoveUnreachableBlocks(F);
EverChanged |= IterativeSimplifyCFG(F);
// If neither pass changed anything, we're done.
if (!EverChanged) return false;
// IterativeSimplifyCFG can (rarely) make some loops dead. If this happens,
// RemoveUnreachableBlocks is needed to nuke them, which means we should
// iterate between the two optimizations. We structure the code like this to
// avoid reruning IterativeSimplifyCFG if the second pass of
// RemoveUnreachableBlocks doesn't do anything.
if (!RemoveUnreachableBlocks(F))
return true;
do {
EverChanged = IterativeSimplifyCFG(F);
EverChanged |= RemoveUnreachableBlocks(F);
} while (EverChanged);
return true;
}

100
llvm/test/Transforms/SimplifyCFG/iterative-simplify.ll Normal file
View File

@ -0,0 +1,100 @@
; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | not grep bb17
; PR1786
define i32 @main() {
entry:
%retval = alloca i32, align 4 ; <i32*> [#uses=1]
%i = alloca i32, align 4 ; <i32*> [#uses=7]
%z = alloca i32, align 4 ; <i32*> [#uses=4]
%z16 = alloca i32, align 4 ; <i32*> [#uses=4]
%"alloca point" = bitcast i32 0 to i32 ; <i32> [#uses=0]
store i32 0, i32* %i
%toBool = icmp ne i8 1, 0 ; <i1> [#uses=1]
br i1 %toBool, label %cond_true, label %cond_false
cond_true: ; preds = %entry
store i32 0, i32* %z
br label %bb
bb: ; preds = %cond_next, %cond_true
%tmp = load i32* %z ; <i32> [#uses=1]
%tmp1 = sub i32 %tmp, 16384 ; <i32> [#uses=1]
store i32 %tmp1, i32* %z
%tmp2 = load i32* %i ; <i32> [#uses=1]
%tmp3 = add i32 %tmp2, 1 ; <i32> [#uses=1]
store i32 %tmp3, i32* %i
%tmp4 = load i32* %i ; <i32> [#uses=1]
%tmp5 = icmp sgt i32 %tmp4, 262144 ; <i1> [#uses=1]
%tmp56 = zext i1 %tmp5 to i8 ; <i8> [#uses=1]
%toBool7 = icmp ne i8 %tmp56, 0 ; <i1> [#uses=1]
br i1 %toBool7, label %cond_true8, label %cond_next
cond_true8: ; preds = %bb
call void @abort( )
unreachable
cond_next: ; preds = %bb
%tmp9 = load i32* %z ; <i32> [#uses=1]
%tmp10 = icmp ne i32 %tmp9, 0 ; <i1> [#uses=1]
%tmp1011 = zext i1 %tmp10 to i8 ; <i8> [#uses=1]
%toBool12 = icmp ne i8 %tmp1011, 0 ; <i1> [#uses=1]
br i1 %toBool12, label %bb, label %bb13
bb13: ; preds = %cond_next
call void @exit( i32 0 )
unreachable
cond_false: ; preds = %entry
%toBool14 = icmp ne i8 1, 0 ; <i1> [#uses=1]
br i1 %toBool14, label %cond_true15, label %cond_false33
cond_true15: ; preds = %cond_false
store i32 0, i32* %z16
br label %bb17
bb17: ; preds = %cond_next27, %cond_true15
%tmp18 = load i32* %z16 ; <i32> [#uses=1]
%tmp19 = sub i32 %tmp18, 16384 ; <i32> [#uses=1]
store i32 %tmp19, i32* %z16
%tmp20 = load i32* %i ; <i32> [#uses=1]
%tmp21 = add i32 %tmp20, 1 ; <i32> [#uses=1]
store i32 %tmp21, i32* %i
%tmp22 = load i32* %i ; <i32> [#uses=1]
%tmp23 = icmp sgt i32 %tmp22, 262144 ; <i1> [#uses=1]
%tmp2324 = zext i1 %tmp23 to i8 ; <i8> [#uses=1]
%toBool25 = icmp ne i8 %tmp2324, 0 ; <i1> [#uses=1]
br i1 %toBool25, label %cond_true26, label %cond_next27
cond_true26: ; preds = %bb17
call void @abort( )
unreachable
cond_next27: ; preds = %bb17
%tmp28 = load i32* %z16 ; <i32> [#uses=1]
%tmp29 = icmp ne i32 %tmp28, 0 ; <i1> [#uses=1]
%tmp2930 = zext i1 %tmp29 to i8 ; <i8> [#uses=1]
%toBool31 = icmp ne i8 %tmp2930, 0 ; <i1> [#uses=1]
br i1 %toBool31, label %bb17, label %bb32
bb32: ; preds = %cond_next27
call void @exit( i32 0 )
unreachable
cond_false33: ; preds = %cond_false
call void @exit( i32 0 )
unreachable
cond_next34: ; No predecessors!
br label %cond_next35
cond_next35: ; preds = %cond_next34
br label %return
return: ; preds = %cond_next35
%retval36 = load i32* %retval ; <i32> [#uses=1]
ret i32 %retval36
}
declare void @abort()
declare void @exit(i32)